Apparatus for increasing the arc voltage in relation to the particular number of spark gaps which define the threshold characteristics in magnetically blown surge arrestors

ABSTRACT

A magnetically blown surge arrester is comprised of a plurality of superposed arc chambers each including a pair of spaced horns providing a sparkover gap. The horns of a lower chamber are provided with projections which extend into the chamber nextabove that are contacted by the arc as it is blown after being struck between the horns of the latter chamber, and the arc is then struck between the horns in the lower chamber following a passage of charge carriers from the upper to the lower chamber.

United States Patent [151 3,686,532 Rudolph et al. 145] Aug. 22, 1972 [54] APPARATUS FOR INCREASING THE ARC VOLTAGE IN RELATION TO THE PARTICULAR NUMBER OF SPARK GAPS WHICH DEFINE THE THRESHOLD CHARACTERISTICS IN MAGNETICALLY BLOWN SURGE ARRESTORS Inventors: Rene Rudolph, Zurich; Tjhing Thian Tan, Baden, both of Switzerland Assignee: Aktiengesellschait Brown, Boveri & Cie., Baden, Switzerland Filed: I May 7, 1971 Appl. No.: 141,188

Foreign Application Priority Data May 12, 1970 Switzerland ..7011/70 us. Cl ..317/70, 315/36 rm. c1. .uozn 9/06 Field of Search ..315/36; 317 70 [5 6] References Cited UNITED STATES PATENTS 3,504,226 3/1970 Stetson ..317/70 X 3,524,099 8/ 1970 Stetson ..315/36 Primary Examiner-James D. Trammell Attorney-Pierce, Scheffler & Parker ABSTRACT 8 Claims, 6 Drawing Figures Patented Aug. 22, 1972 6 Sheds-Sheet 1 Fig.1

Patented Aug. 22, 1972 6 SheetsSheet 3 Patented Aug. 22, 1972 3,686,532

6 Sheets-Sheet 3 Patented Aug. 22, 1972 6 SheetsSheet 4 Fig.4

Patented Aug. 22 1972 6 Sheets-Sheet 5 Patemed Aug. 22, 1912 3,686,532

6 Sheets-Sheet 6 APPARATUS FOR INCREASING THE ARC VOLTAGE IN RELATION TO THE PARTICULAR NUMBER OF SPARK GAPS WHICH DEFINE THE THRESHOLD CHARACTERISTICS IN MAGNETICALLY BLOWN SURGE ARRESTORS high are voltage to be obtained. One or more blow-out coils, shunted by a resistor orspark gap, are serially connected to the arrester spark gaps to provide a sufficiently powerful blowing action. The discharge current, which briefly rises to a high value, must be conducted through the elements which shunt the blow-out coil, and, in the form of a follow-up current, must then be rapidly commutated to the blow-out coil to ensure a reliable blow-out action. I

It is also the practice in modern arresters for the individual spark gaps to be controlled so as to impose a defined .but unequal voltage distribution thereon thus permitting a sensible reduction of the sparkover voltage. However, it is a disadvantage that these measures are insufficient for a very low relative protection level which refers to the maximum possibly occurring arrester voltage in terms of the nominal arrester voltage. In this case it is necessary for each individual spark gap to be provided with complex pre-ionization means so that the sparkover voltage and the dispersion zone thereof can be maintained at a sufficiently small value. The previously mentioned control and ionization elements will however render the final product substantially more costly.

The protection level of the arresters can be reduced in accordance with the increase in the ratio between arc voltage and sparkover voltage. Discounting the above mentioned defined unequal voltage distribution, this ratio can be increased through a reduction of the inherent sparkover voltage of the individual spark gaps by reducing the flashover distance thereof. However, this method of solving the problem is questionable because it results in an increase of the sparkover voltage dispersion zone. It is also possible for the previously mentioned ratio to be increased by adopting a novel method for lengthening the arc in the arrester arc gap chamber so that the arc voltage is raised to an exceptionally high value.

It is the object of the invention to increase the arc voltage in each spark gap to a hitherto unknown value by a novel are elongation in accordance with the invention.

The reduction in the number of arc gaps thus achieved on the one hand permits the protection level of the arresters to be reduced, on the other hand it is possible to save control and ionization elements, thus reducing the cost of the final product.

These advantages may be obtained fundamentally by increasing the diameter of the extinction chamber,

resulting in an increase in the maximum arc length and in a corresponding increase of the arc voltage. However, given the same follow-up current and the same which defines the blowing of the arc since the length of path of the magnetic field lines would increase with a corresponding increase of the blowing coil diameter.

Since the blowing coil would have to enclose a larger surface area, the inductance of the coil would simultaneously increase and commutation of the follow-up current from the shunting spark gap or from the shunting resistor to the blowing coil would be substantially delayed. Although it would be possible to eliminate the increase of inductance by adopting a smaller number of turns, this would result in a further reduction of the magnetic induction which is proportional to the number of turns and the entire operation of magnetic blowing would thus become doubtful.

The problem outlined hereinbefore is solved in accordance with the invention in that the arc is lengthened by suitable means so that it is transferred from a first chamber, comprising bottom, cover and a cylindrical wall connecting said bottom and cover, into a second or several successive chambers, said chambers being preferably arranged one above the other.

The chambers are provided with apertures for establishing an electrical connection to the next chamber.

The system according to the invention ensures that the arc, having'progressed to the limiting walls of the first chamber and being thus lengthened, is drawn into the second chamber, preferably disposed thereabove or therebelow, in which second chamber the are also extends subsequently to the edges where it terminates, depending on the construction of the chamber, or in order to extend still further in a third or fourth chamber. The are voltage for each sparkover spot will then be greater by a multiple than it would be if each chamber were to be provided with its own spark gap. The elimination of a plurality of arc gaps enables the number of control and ionization elements to be corto the next chamber, the first chamber being also pronumber of turns for the blowing coil, this would result in a corresponding reduction of the magnetic induction vided with horns of an arrester spark gap, which defines the sparkover voltage, the are being initially struck between said horns.

The next adjoining chamber is provided with electrically conducting auxiliary horns on which projections are mounted, preferably disposed on the chamber edge and adapted to extend into the precedingly disposed chamber through apertures thereof. An ionization duct, terminating between the auxiliary horns is also provided and extends from the aforementioned chamber to the precedingly disposed chamber. The voltage gradient of the lengthened arc ensures that a potential difference occurs between the projections and therefore also between the auxiliary horns, but this potential difference is generally not sufficient in order to strike the sparkover spot of the auxiliary horns in the second chamber. Nevertheless, owing to the progress of the arc to the walls defining the first chamber, sufficient charge carrier will pass through the ionization duct to the sparkover spot of the auxiliary horns in order to produce flashover thereat, thus extinguishing the arc portion in the first chamber between the projections which extend into said chamber. The arc in the second chamber may then further extend from the struck sparkover spot of the auxiliary horns so that the greatly elongated arc comprises three parts in this state, two of the parts continuing to burn in the first chamber between one horn of the arrester spark gap and a projection extending into this chamber and being associated with the auxiliary horns of the next chamber. The third portion of the arc is identical to the previously mentioned are which extends from the struck sparkover spot of the auxiliary horns into the next chamber. The elongation of the are by transfer from the first chamber to the next can be repeated at will until the restriking limit is reached. It is therefore advantageous if a known curvilinear construction of the chamber bottoms and tops is employed in order to increase the restrike withstandability.

The previously mentioned ionization duct, which extends from one chamber to the next, permits striking of the auxiliary horns if the voltage between them is not excessive without resulting in an excessively low voltage withstandability of the aforementioned sparkover spot when the arc subsequently extends further into the next chamber.

The previously described cascade spark gap system with successive chambers therefore results in a greatly increases arc voltage, only the first spark gap of the spark gap cascade defining the sparkover voltage of the surge arrester.

According to a further embodiment of the invention, the arc does not extend radially but burns between two concentric and circular chamber walls which extend from the struck horns of the arrester spark gap. To this end, the arc extends between the aforementioned concentric circular walls in semicircular manner in one plane, which, to increase the restrike withstandability between parallel extending arc portions is preferably so curved that there is no visual connection between the concentric arc parts of the arc which extends in semicircular manner. In a system similar to that already mentioned, the arc is drawn from a first chamber into a next chamber, not disposed in the same plane, in order to extend still further thereat between two concentric circular walls.

It is possible to avoid the mechanism for the are being drawn into the next chamber if the preferably curvilinear plane between the two concentric circular walls is constructed in spiral form.

The inner concentric circular wall can be reduced to such an extent so that in an extreme case it is replaced merely by one of the two horns of the arrester spark gap. Said horn will then be constructed axially, preferably cylindrically, in the middle of the spiral arc expansion plane.-

According to a further preferred embodiment of the invention, one of the two horns of the spark gap of the first chamber is constructed in cylindrical form and the other horn of the spark gap is so disposed as to partially surround the first concentrically and at a distance.

Normally, the arc will be maintained for the longest period near the edge of the chamber. The energy absorption capacity of the chamber is therefore relatively limited because the chamber material is rapidly heated at this place, the arc is less readily cooled, and the arc voltage therefore diminishes. If the sparkover spot between the horns of the arrester spark gap' is restruck after the arc has reached the edge of the last chamber, the arc which has already been expanded will be extinguished and the fresh arc in the first chamber must then once again travel from the sparkover spot of the arrester spark gap to the chamber wall of the last chamber. In this way it is possible to utilize the thermal capacity of the entire chamber and not only the edge zone thereof. Heating of the entire chamber surface instead of only the edge zone thereof enables the energy absorption capacity of the individual chamber to be substantially increased. The previously mentioned restriking of the sparkover spot in the arrester spark gap may therefore be achieved, according to a further embodiment of the invention, in that an ionization duct extends from the chamber edge of the last chamber to the sparkover spot of the arrester spark gap of the first chamber and by means of which the sparkover spot in said chamber is restruck.

It is particularly advantageous to provide a preionization element at only one sparkover spot of the cascade circuit.

Self-extinguishing dc. voltage arresters require an extremely high arc voltage and for this reason the system according to the invention has a particular significance for such apparatus owing to the exceptional elongation of the arc.

Embodiments of the invention are illustrated in the accompanying drawings in which:

FIG. 1 is a diagram of a spark gap system with two chambers and a blowing coil with a shunt resistor:

FIG. la illustrates a blowing coil system with a shunt spark gap;

FIGS. 2-5 illustrate different embodiments of spark gap systems and;

FIG. 6 is a section through a chamber along the line 6-6 of FIGS.

Identical parts in the individual illustrations are provided with the same reference numerals.

All design features not required for a direct understanding of the invention have been omitted from the illustrations. According to FIG. 1, the numeral 1 refers to a first chamber and the numeral 2 to a second chamber in a spark gap system in which the chambers may be arranged in a superposed manner. The interior surfaces of the cylindrical walls 14 which define the chambers 1 and 2, respectively are provided with portions 3 which project in a radially inward direction so as to lengthen the path of the are which is expanded into contact with the chamber wall by a magnetically induced blowing effect. The chamber 1 is provided with horns 4 of the arrester spark gap, the sparkover spot 12 of the arrester spark gap being disposed between these horns. The chamber 2 is provided with auxiliary horns 5 having projections 6 which which extend outwardly from chamber 2 and enter the chamber 1 adjacent-its periphery through apertures 7 provided in the end wall of the first chamber 1 when the chambers are stacked one above the other. An ionization duct 8 extends from the first chamber 1 into the second chamber 2.

A blowing coil 9 with a shunt resistor is also associated with the first chamber 1. However, the blowing coil system according to FIG. 11a may also comprise a blowing coil 9 and a shunt spark gap 11. A sparkover spot 13 of the auxiliary horn 5 is disposed between the auxiliary horns 5 of the second chamber 2.

FIG. 2 shows another embodiment of the invention which is similar in most respects to FIG. 1 except that there is a slightly different configuration of the horns 4 of the arrester spark gap and of the auxiliary horns 5 with the projections 6 and the associated apertures 7 as well as the ionization duct 8 which extends from the first chamber 1 into the second chamber 2.

In a further embodiment as depicted in FIG. 3, each of the chambers 1 and 2 is provided with a centrally located wall portion 14' around which the blown are also extends, this portion of the chamber wall also being provided with radially outward projections to increase the length of the arc path around it. A further rib-like wall portion 14" extends from the centrally located wall portion 14 to the peripheral wall portion 14 to establish a barrier between horns 4-4 and the projections 6 extending from horns 5 into chamber 1.

In the two embodiments illustrated respectively in FIGS. 4 and 5 one of the horns 4 of thearrester spark gap is constructed in cylindrical form and extends from the center of the first chamber 1 into the second chamber 2. In this system, a part 14 of the chamber wall 1 4 at one position of the arrester spark gap is also extended to the cylindrically constructed horn 4 to establish a barrier between the other horn 4 and the single projection 6 from born 5 in chamber 1. A similar barrier wall 14"" is provided in the other chamber 2 at one side of horn 5 to ensure expansion of the arc in the proper direction in that chamber.

In FIG. 5 one of the two horns 4 in the first chamber 1 is so constructed as to partially surround the second cylindrically constructed born 4 at a defined distance. The sparkover spot 12 of the arrester spark gap is disposed between the two horns 4.

FIG. 6 shows the manner in which the chamber bottom between the chamber walls 14 is curved.

The method of operation of an arrester spark gap according to the invention is described hereinbelow.

The chambers 1 and 2, preferably disposed one above the other are connected via the lead 15 in parallel to an object which is to be protected against surge voltages. Arrester resistors, control elements and the like, also required, have been omitted because they are obvious to an expert in this art and haveno significance with respect to the invention. Part of the voltage applied to the object to be protected is applied to the horns 4 of the arrester spark gap of the first chamber 1. If a sufficiently high surge voltage occurs, the first chamber 1 will come into operation, that is to say a short arc will initially be established at the sparkover spot 12 between the horns 4 of the arrester spark gap, accompanied by a briefflow of heavy discharge current through the short arc and the shunt element 10 or 11 of the blowing coil 9, this current being rapidly commutated to the blowing coil in the form of a so-called follow-up current. When the followup current passes through the blowing coil 9, a strong magnetic blowing action will be exerted onto the are established between the horns 4 of the arrester spark gap.

The magnetic blowing action onto the arc causes the arc to be continuously elongated from the two horns 4 until it finally expands into contact with the inner surface of the chamber wall 14, the course of the arc having a meandering configuration as it passes around the radially inward projecting wall portions 3. The expanded are also comes into contact with 6 which extend through the apertures 7 into chamber 1 adjacent the wall 14. The auxiliary horns 5, mounted on the projections 6 of the second chamber 2, will now have a potential which is equal to the voltage of the arc in the first chamber 1 between the apertures 7 forthe projections 6. This voltage will, however, be insufficient to cause the sparkover spot 13 between the auxiliary horns 5 in the second chamber 2 being struck. However, a sufficient number of charge carriers will pass through the ionization duct 8, extending from the first chamber 1 into the second chamber 2, to reach the sparkover spot 13 of the auxiliary horns 5 in the second chamber 2 in order to cause a flashover at that place thus extinguishing that part of the arc in the first chamber 1 which is disposed between the projections 6 extending into said chamber 1. The arc may then elongate in the second chamber 2 from the struck sparkover spot 13 of the auxiliary horns 5, so that in this state the greatly elongated arc consists of three parts, two of which continue to burn in the first chamber 1 respectively between a horn 4 of the arrester spark gap and a corresponding projection 6 of the auxiliary horn 5 of the next chamber, this projection extending into the chamber, and the third part continues to elongate in the chamber 2 from the struck sparkover spot 13 of the auxiliary horns 5.

The restrike withstandability will be increased if the chamber bottom of the chambers 1 and 2 has a curvature 16 as shown for example in FIG. 6. In this embodiment, the arc does not expand radially but rather along a circular path between the two concentric wall 14 and 14', starting from the horns 4 of the arrester spark gap, as in FIG. 3. Essentially the same type of arc expansion from horns 4 along a circular path is obtained in the embodiments of FIGS. 4 and 5 wherein one of the horns 4 occupies a central position in the chambers l and 2. The curvature 16 of the chamber bottom is so constructed that no line-of-sight exists between the concentric are parts of the arc expanding along the circular path. Accordingly, the restrike withstandability between the parallel parts of the arc is increased.

If the chamber bottom 16, which is preferably curved, is constructed in spiral form between the two concentric and circular chamber walls 14 it is possible to avoid the mechanism for the are being drawn into the next chamber.

We claim:

1. In a surge voltage arrester of the type wherein the are drawn between horns located in an arrester chamber and electrically connected in parallel with the electrical component to be protected is magnetically blown and simultaneously elongated in the chamber, the combination comprising first and second are receiving chambers arranged in superposed relation, spaced arcing horns located in said first chamber and between which an arc is initially struck upon occurrence of the surge voltage and thereafter elongated along the wall of the chamber, spaced arcing horns located in said second chamber and between which the arc is also struck and thereafter elongated along the chamber wall subsequent to elongation of the arc in said first chamber, an ionization duct extending from said first chamber into the second chamber in the vicinity of the response point intermediate the arcing horns of said second chamber, said response point between said arcing horns in said second chamber prior to striking of the arc therebetween being parallel to a part of the elongated are which burns between the horns in said first chamber, and at least one conductive projection extending from a horn in said second chamber into said first chamber for electrically connecting a point on the elongated arc in said first chamber with the horn in said second chamber.

2. A surge voltage arrester defined in claim 1 wherein the arcing horns in said first and second chambers are constituted by structurally separate pairs of horns and wherein two of said conductive projections are provided and extend respectively from the horns in said second chamber into said first chamber for electrically connecting respective points on the elongated arc in said first chamber with the horns in said second chamber.

3. A surge voltage arrester as defined in claim. 2 wherein said are is elongated in said first chamber by radial expansion into contact with the chamber wall so as to extend around the inner surface thereof and said conductive projections which extend from the horns in said second chamber into said first chamber are located in spaced relation along a portion of the path of the elongated arc in said first chamber.

4. A surge voltage arrester as defined in claim 2 wherein said first and second chambers include a centrally located wall part and a rib-like barrier wall extending from said central wall part to the surrounding wall of the corresponding chamber, the pair of horns in said first chamber being located to one side of said ribinterior of said first chamber between the said centrally located wall part and the outer boundary wall of the chamber has a convex configuration of such height that no line-of-sight exists between any points on the respective paths of the arcs along the surfaces of said centrally located wall part and the outer boundary wall of the chamber.

6. A surge voltage arrester as defined in claim 1 wherein an arcing horn in said first chamber and a corresponding arcing horn in said second chamber are structurally integrated into a cylindrically configured part located centrally within and extending between said first and second chambers, wherein the other horn in said first chamber is located at one side of a rib-like barrier wall extending between said centrally located cylindrically configured horn and the interior boundary wall of said chamber, and wherein said conductive proiflfi ii fi id ll i1%r3liii$a& i ?3?%$! posite side of said rib-like barrier wall in the path of the arc.

7. A surge voltage arrester as defined in claim 6 wherein said other horn in said first chamber includes an arcuate portion extending partially around said cylindrically configured horn.

8. In a surge voltage arrester of the type wherein the are drawn between horns located in an arrester chamber and electrically connected in parallel with the electrical component to be protected is magnetically blown and simultaneously elongated in the chamber, the combination comprising first and second arc receiving chambers arranged in superposed relation, first and second spaced arcing horns located in said first chamber and between which an arc is initially struck upon occurrence of the surge voltage, said second horn having a cylindrical configuration located centrally within the first chamber and which extends also into said second chamber, and the walls defining said first and second chambers including inclined portions such as to direct the are after being struck between said horns in said first chamber and thereafter elongated along and around the wall thereof into said second chamber for further elongation along and around the wall thereof, one end of the are then being anchored on said first horn in said first chamber and the other end of said are being anchored on said second horn in said second chamber. 

1. In a surge voltage arrester of the type wherein the arc drawn between horns located in an arrester chamber and electrically connected in parallel with the electrical component to be protected is magnetically blown and simultaneously elongated in the chamber, the combination comprising first and second arc receiving chambers arranged in superposed relation, spaced arcing horns located in said first chamber and between which an arc is initially struck upon occurrence of the surge voltage and thereafter elongated along the wall of the chamber, spaced arcing horns located in said second chamber and between which the arc is also struck and thereafter elongated along the chamber wall subsequent to elongation of the arc in said first chamber, an ionization duct extending from said first chamber into the second chamber in the vicinity of the response point intermediate the arcing horns of said second chamber, said response point between said arcing horns in said second chamber prior to striking of the arc therebetween being parallel to a part of the elongated arc which burns between the horns in said first chamber, and at least one conductive projection extending from a horn in said second chamber into said first chamber for electrically connecting a point on the elongated arc in said first chamber with the horn in said second chamber.
 2. A surge voltage arrester defined in claim 1 wherein the arcing horns in said first and second chambers are constituted by structurally separate pairs of horns and wherein two of said conductive projections are provided and extend respectively from the horns in said second chamber into said first chamber for electrically connecting respective points on the elongated arc in said first chamber with the horns in said second chamber.
 3. A surge voltage arrester as defined in claim 2 wherein said arc is elongated in said first chamber by radial expansion into contact with the chamber wall so as to extend around the inner surface thereof and said conductive projections which extend from the horns in said second chamber into said first chamber are located in spaced relation along a portion of the path of the elongated arc in said first chamber.
 4. A surge voltage arrester as defined in claim 2 wherein said first and second chambers include a centrally located wall part and a rib-like barrier wall extending from said central wall part to the surrounding wall of the corresponding chamber, the pair of horns in said first chamber being located to one side of said rib-like barrier wall and said conductive projections which extend from the horns in said second chamber into said first chamber are located at the opposite side of said rib-like barrier wall in spaced relation along that portion of the path of the elongated arc in said first chamber which extends along the face of said rib-like barrier wall.
 5. A surge voltage arrester as defined in claim 4 wherein the portion of the bottom boundary wall of the interior of said first chamber between the said centrally located wall part and the outer boundary wall of the chamber has a convex configuration of such height that no line-of-sight exists between any points on the respective paths of the arcs along the surfaces of said centrally located wall part and the outer boundary wall of the chamber.
 6. A surge voltage arrester as defined in claim 1 wherein an arcing horn in said first chamber and a corresponding arcing horn in said second chamber are Structurally integrated into a cylindrically configured part located centrally within and extending between said first and second chambers, wherein the other horn in said first chamber is located at one side of a rib-like barrier wall extending between said centrally located cylindrically configured horn and the interior boundary wall of said chamber, and wherein said conductive projection extending from the other horn in said second chamber into said first chamber is located at the opposite side of said rib-like barrier wall in the path of the arc.
 7. A surge voltage arrester as defined in claim 6 wherein said other horn in said first chamber includes an arcuate portion extending partially around said cylindrically configured horn.
 8. In a surge voltage arrester of the type wherein the arc drawn between horns located in an arrester chamber and electrically connected in parallel with the electrical component to be protected is magnetically blown and simultaneously elongated in the chamber, the combination comprising first and second arc receiving chambers arranged in superposed relation, first and second spaced arcing horns located in said first chamber and between which an arc is initially struck upon occurrence of the surge voltage, said second horn having a cylindrical configuration located centrally within the first chamber and which extends also into said second chamber, and the walls defining said first and second chambers including inclined portions such as to direct the arc after being struck between said horns in said first chamber and thereafter elongated along and around the wall thereof into said second chamber for further elongation along and around the wall thereof, one end of the arc then being anchored on said first horn in said first chamber and the other end of said arc being anchored on said second horn in said second chamber. 